Kyle Forsythe, left, and Robby Hartpence, both field technicians for TREKK Design Group LLC, Kansas City, Mo., participate in a city sewer system test demonstration using smoke on Sept. 3, 2013. The test involved filling the sewer system, which may cause smoke to come out of manhole covers or even the roof vents of peoples' homes. That may cause people to mistakenly think their house is on fire.

Smoke coming out of your toilet is never a good thing, but in a few areas of Lawrence in coming weeks, it may not be as concerning as you would think.

City officials on Tuesday were alerting residents that they may begin seeing harmless smoke in a variety of places in their homes and yards as the city embarks on a nearly $20 million project to improve the community’s sewer system.

“Don’t panic,” said Jeanette Klamm, a spokeswoman for the city’s utility department.

The smoke will be caused by private contractors pumping non-toxic smoke into city sewer lines. The crews then monitor where the smoke comes out, and use that information to determine where the city’s large underground sewer pipes might be leaking.

Neighborhoods near the Ninth and Emery area in central Lawrence, and neighborhoods east and north of 23rd and Haskell will be the first to experience the smoke testing, which is expected to begin in about a week.

In many cases, the testing might result in smoke escaping into people’s homes. If a system is relatively free of leaks, the smoke should come out the vent pipes that run through the roofs of many homes. But in other cases, homeowners may see smoke coming out of floor drains, sump pumps, or even from underneath their toilets.

Cliff Cate, a project manager for the city-hired contractor TREKK Design Group, said it is not uncommon for the wax ring of a toilet to shrink and allow a place for the smoke to escape. That means the wax ring is allowing sewer gas to seep into the home as well.

“What we end up seeing with these tests really kind of depends on the age of the home,” Cate said.

Klamm stressed that the white smoke is non-toxic and can be cleared out of a home by simply opening a window.

“It doesn’t leave any residue or smell,” Klamm said.

City officials also will be doing their best to make sure the smoke doesn’t come as a surprise. Crews will hang a notice on the door of each residence or business 48 to 72 hours before testing begins in a neighborhood. Road signs announcing that smoke testing is underway also will be placed in neighborhoods. That’s to help reduce the number of calls motorists may make to the fire department after driving by a property where they see smoke, Klamm said.

Sometimes the smoke does happen outside the home. Smoke in ditches or in yards is common when a buried sewer line has a leak or defect. Those outside occurrences of smoke are mainly what crews are trying to document. No one with TREKK or the city will be seeking to do interior home inspections unless the homeowner requests one.

Mike Lawless, the city’s deputy director of utilities, said if homeowners have smoke in their homes and see crews outside, crew members will be happy to look at the situation. But the focus of the project is figuring out where the city should spend its money repairing leaky sewer lines.

The leaky lines allow large amounts of water to enter the sewer system during rainstorms. That water then gets transported to the city’s sewage treatment plant, where it costs the city millions of dollars to treat and release.

The Environmental Protection Agency already has put the city on notice that the city’s sewage treatment plant may have problems meeting the EPA’s wet weather regulations if the storm water inflow problem isn’t addressed.

Previously, the city has estimated it could spend $40 million or more upgrading pipes, pump stations and other infrastructure. Now, the city is hoping to spend about half of that amount on a program that aims to reduce the amount of water seeping into the system in the first place.

“We can either make the pipes bigger to handle all the water, or we can try to reduce the amount of water that goes through the pipes to begin with,” Lawless said.

The project is expected to take eight years, and will involve testing and repairs in most of the neighborhoods east of Iowa Street and north of 31st Street. But for 2013, testing will be concentrated in two areas:

• An area generally bounded by Ninth Street, University Drive, High Drive and West Campus Road.

• An area generally bounded by Haskell Avenue, 23rd Street, 12th Street and the eastern city limits.

Testing in both areas should conclude by the end of October, city officials estimated.

The first round of testing will be near about 1,000 homes or structures and will inspect about 60,000 feet of pipe. The entire eight-year project is expected to be near about 9,000 homes or structures and test about 590,000 feet of pipe.